Garmin GPS Accuracy

 

Haven't spent much time with you guys for a while. Recently move to KY, and found my Garmin GPS hasn't been close for many POI or general address loctions since being here. Any ideas why ?

more info needed

dweveritt wrote:

Haven't spent much time with you guys for a while. Recently move to KY, and found my Garmin GPS hasn't been close for many POI or general address loctions since being here. Any ideas why ?

Which Garmin unit do you have?

Sensor chips have been changed in the Garmin units so some are more accurate than others.

It also may be a problem with your unit.

--
http://www.poi-factory.com/node/21626 - red light cameras do not work

bad data

dweveritt wrote:

..Any ideas why ?

Sounds just like bad address data. Not all that untypical for Garmin. I have a friend who's house is several blocks down the street from where the GPS claims it is based on the address. Not every address is in the system, they interpolate a lot, but in this case the actual address is at the opposite end of a street, so it's not an interpolation issue, it is bad data.

MY unit is a 660, about a

MY unit is a 660, about a year old. Didn't have much of a problem until KY. Didn't down load the 2008 updates, would they make a differance.

.

Its not "bad" data, its just how addresses are calculated by the units. POI addresses are not actually plotted, the unit just guesses where the address is located on the street using an algorithm.

There are a couple of prior threads discussing this issue.

Rural area?

dweveritt wrote:

Haven't spent much time with you guys for a while. Recently move to KY, and found my Garmin GPS hasn't been close for many POI or general address loctions since being here. Any ideas why ?

Like any business, the most attention will go to where the greatest number of customers (or potential customers) are. If you moved to a more rural area, it will typically be longer between useful map updates than in more high-traffic areas.

Check Google maps

I think that Google maps is pretty much the same maps check your locations by address and see if it is also off. My House is off by about a half mile. I have written to navteq many times...and they dont seem to fix it. My road is not new..1800's way before cars..and is all messed up. It is the old computer story Garbage in Garbage out..

--
Dave_ Nuvi 660 , 760,1490LMT Wooster, Ohio

Please tell us more

GadgetGuy2008 wrote:

Its not "bad" data, its just how addresses are calculated by the units. POI addresses are not actually plotted, the unit just guesses where the address is located on the street using an algorithm.

I'm very interested in this. Perhaps you could explain an algorithm that could put a house, as it did for my friend's house, at the completely wrong end of a street several city blocks long (about .4 mile) rather than at the other end of the street where it belongs without the data being incorrect. To be clear, it placed him before the very first house on the street, when he is actually the second to last house on the street. And the house numbers on the street do run in order.

The GPS is probably accurate, the maps are not

As Zecpull stated, GI-GO.... There is a small town in a rural area near me that I went through often and the map shows that I was one block vertically and 1 block horizontally off from where I really was. The Lat/Lon coordinates were actually right, it is the map that was skewed. They eventually got the map fixed. I live on a street that is only 5 houses long. The way Navteq determines addresses is to assign a block number and then divide it into 100 segments. They say that this will "sometimes" skew the address to the wrong end of the block. Since my address is only "4" it shows me at the low end of the block, Google Maps does the same thing. At least you can see my house from where the GPS says it should be. To be fair, the folks (Navteq) who develop and maintain the map database have taken on a monumental project. New streets and roads are constantly being built or re-rerouted. House numbering schemes vary from neighborhood to neighborhood. For now, they have a model that everything must fit, right or wrong. Hopefully in time, they may be able to refine this model so that true addresses show up where they really are on the map. Is the GPS right? You bet! The map is the culprit.

--
"There's no substitute for local knowledge" nüvi 750, nüvi 3597

My folks and brother

Several years ago in rural ND they changed the addressing system to streets and house numbers from the old rural system. My parents house shows up on a GPS about 10 miles from the actual house location. Same for my brothers house.

And to think, the reason for the change was so that emergency responders would have a easier time finding these addresses. I sure hope THEY don't rely on GPS. Many people have gotten lost trying to find my parent's house using GPS including the satellite guy, phone company guy, and several hired hands looking to report for work.

Could be both

At least my Garmin Nuvi 200 accuracy stinks. I was on the service road and it was at least 70 feet from the highway and it was still showed the opposite.

Jeff

.

.

dweveritt wrote:Haven't

dweveritt wrote:

Haven't spent much time with you guys for a while. Recently move to KY, and found my Garmin GPS hasn't been close for many POI or general address loctions since being here. Any ideas why ?

Two things strike me: You have moved and have (maybe?) a lack of accuracy. Have you tried a master resetting of your GPS?

--
Nüvi 765T, Nüvi 1390T, Nüvi 2559 and 2695 LMT, GPS12, GPS18 (used in nRoute and Oziexplorer on laptop), GPSmap76CSx, SonyEricsson X1 (For OziExplorer CE maps)

"Master Resetting" ? what is

"Master Resetting" ? what is that. We've been traveling between AR, CO and OH for several years without many issues, until KY, where we are staying now. Almost like who ever plotted the KY area fell short of understanding their job.

Garmin GPS Accuracy

I have found that some of the problems is the map information. The location of the poi is wrong

mark

.

dweveritt wrote:

"Master Resetting" ? what is that. We've been traveling between AR, CO and OH for several years without many issues, until KY, where we are staying now. Almost like who ever plotted the KY area fell short of understanding their job.

I wonder if Garmin just provides a level of accuracy demanded by the locals (I was one for 22 years). In KY, any directions more specific than "Over yonder" is usually viewed as overkill. wink

--
Nuvi 660 -- and not upgrading it or maps until Garmin fixes long-standing bugs/problems, and get maps to where they are much more current, AND corrected on a more timely basis when advised of mistakes.

Master resetting

dweveritt wrote:

"Master Resetting" ? what is that. We've been traveling between AR, CO and OH for several years without many issues, until KY, where we are staying now. Almost like who ever plotted the KY area fell short of understanding their job.

IF you have turned off your GPS while travelling a long distance, a master resetting will be a possible solution.
During a travel with the GPS on, there will of course be no problem, the almanac will be updated.

--
Nüvi 765T, Nüvi 1390T, Nüvi 2559 and 2695 LMT, GPS12, GPS18 (used in nRoute and Oziexplorer on laptop), GPSmap76CSx, SonyEricsson X1 (For OziExplorer CE maps)

Accuracy - Known monument locations

I recall seeing brass "monuments" embedded in rocks at prominent locations. I assume these are precisely known locations and could be used to check accuracy.

Anyone know of a POI file of monuments? I'm in the Seattle area if anyone local knows.

.

If you go to Geocaching.com, they have a section on Benchmarks.

Odd and Even Addresses not across from each other

GPS maps also seem to have a problem when the street addresses on the left-hand side of a street are in a different sequence than on the right-hand side. I had to purposely alter the destination address for my route to work so that when I made the final turn where I would expect to receive the "you have" arrived checkered flag, I was still seeing the yards to go being countdown. When I changed the final digit of the address, that was the trick to fool it into announcing I had arrived when in fact I actually did.

--
TomTom One 125, One 140S, Via 1500 and iPhone TomTom App

Huh?

nuvic320 wrote:
dweveritt wrote:

Haven't spent much time with you guys for a while. Recently move to KY, and found my Garmin GPS hasn't been close for many POI or general address loctions since being here. Any ideas why ?

Which Garmin unit do you have?

Sensor chips have been changed in the Garmin units so some are more accurate than others.

It also may be a problem with your unit.

Sensor chips? How about the map data!

GPS receivers with WAAS (Wide Area Augmentation System) can the accuracy to less than three meters on average. No additional equipment or any fees are required to take advantage of WAAS.

The map data being on average of two years old make people think their community has been omitted, when actually it hasn't been released yet.

--
Using Android Based GPS.The above post and my sig reflects my own opinions, expressed for the purpose of informing or inspiring, not commanding. Naturally, you are free to reject or embrace whatever you read.

Found a "survey monument" (corrected term used locally)

SilverSableGPS wrote:

I recall seeing brass "monuments" embedded in rocks at prominent locations. I assume these are precisely known locations and could be used to check accuracy.

Anyone know of a POI file of monuments? I'm in the Seattle area if anyone local knows.

After I posted the above, I went looking for a monument. Found one a couple of miles away and checked it out. I laid my Geko on it and recorded the waypoint. Seemed very close but I still need to figure it out in feet.

Next time you "check" a

Next time you "check" a monument, let the GPS lay there for 10-30 minutes. Giving it time to "average" out will give you a much more accurate location.

--
Frank DriveSmart55 37.322760, -79.511267

.

A couple of different things are being discussed in this thread, so I'm going to comment on both of them.

As to addresses, it's important to understand how the addresses are listed on the map. The data doesn't actually include ALL the actual addresses. Streets are broken into segments. On each street segment, the data has a range of addresses.

And then using the rules that apply for that particular area (for example, even on the north and east, odd on the south and west), it attempts to place those addresses along the street segment. The addresses tend to be more accurate in urban area less so in rural areas.

.
As to GPS accuracy, it's important to remember that recreational grade GPS units are typically accurate to 15 - 30 feet or so. You will not get pinpoint accuracy.

MM is right

As usual. Though I believe she left out one bit of info. The GPSr figures the address as she stated, but the addresses are sometimes laid out differently in some areas and the unit has no way of knowing this without outside input. This is just one of the causes for an address to be way off. I am sure there are more, but this would explain the issues states in this thread.

--
Glenn - Southern MD; SP C330 / Nuvi 750 / Nuvi 265WT

sub-urban monument

phranc wrote:

Next time you "check" a monument, let the GPS lay there for 10-30 minutes. Giving it time to "average" out will give you a much more accurate location.

This is a good recommendation but not practical here since it was in the middle of a sidewalk. Hmmm, maybe I could get a shopping cart and set up camp while I wait.

Averaging? Bah, Humbug.

SilverSableGPS wrote:
phranc wrote:

Next time you "check" a monument, let the GPS lay there for 10-30 minutes. Giving it time to "average" out will give you a much more accurate location.

This is a good recommendation but not practical here since it was in the middle of a sidewalk. Hmmm, maybe I could get a shopping cart and set up camp while I wait.

Don't bother.

These aren't survey grade devices that average the readings over a period of time to make a location more accurate by pinpointing the center of the constellation of fixes that are generated over time.

They are simple 8/12/16/20 channel GPS receivers equipped with or without WAAS and they do nothing but take the present calculated position and shove it out to the mapping processes.

--
Currently have: SP3, GPSMAP 276c, Nuvi 760T, Nuvi 3790LMT, Zumo 660T

True, the Garmin positioning

True, the Garmin positioning of the address may be way off, but it isn't the Garmin's fault. Not everywhere is layed out the same, so there could be huge gaps.

If it is a place I go to often or a place I want to remember, I will simply go to Settings, Where Am I?, then save that position, then name it. It will then be saved under Favorites, so it will guide you to the correct spot the next time you go there. Once it is in Favorites, I can go in and add the telephone number. This has helped me, especially if I want to pick up a pizza for take-out, I can call ahead.

My mom's Assisted Living facility is not where the Garmin says it is. If I took the Garmin's way, I wouldn't be able to get there because there is a greenbelt between the facility and the other side of the road. I know how to get there, so I went to Where Am I, and saved it. Then, went to Favorites, and added the telephone number.

This was a huge help while I was out of town. My wife had not been to the facility since my mom just moved in. Had she punched in the address, she wouldn't have gotten there. Since I saved it under my Favorites, she got there and even called to check on my mom before she arrived, which made my mom happy.

This is easy to do, but if there is an easier way, let me know!

A Shortcut to...

bobshort1 wrote:

. . .If it is a place I go to often or a place I want to remember, I will simply go to Settings, Where Am I?, then save that position, then name it. . .

A shortcut to the above on most nuvis is to tap the vehicle icon on the screen and the coordinates will appear. All you need to do from there is save it as a favorite.

--
JRoz -- DriveSmart 55 & Traffic

Thanks. That does work

Thanks. That does work quicker. Less steps, too.

Don't forget to go to

Don't forget to go to Navteq.com and send in a map request to fix it.

--
Nuvi 3790LMT, Nuvi 760 Lifetime map, Lifetime NavTraffic, Garmin E-Trex Legend Just because "Everyone" drives badly does not mean you have to.

GPS Accuracy

I suspect that part of the problem could come from the accuracy of the road drawings that are submitted to whomever, Navteq gets their data. If you look at roads on Google Earth, there is often a line showing where the map says the road is, but the actual photo is a bit different. Usually, it's not a great distance. It could be that "As Built Drawings" were not submitted. Instead, they submitted "Design Drawings" and subtle errors or changes made when the road was built, could possibly be the reason.

Does anyone know for sure?

--
DriveSmart 65, NUVI2555LMT, (NUVI350 is Now Retired)

That sounds right

davidkbrown wrote:

I suspect that part of the problem could come from the accuracy of the road drawings that are submitted to whomever, Navteq gets their data. If you look at roads on Google Earth, there is often a line showing where the map says the road is, but the actual photo is a bit different. Usually, it's not a great distance. It could be that "As Built Drawings" were not submitted. Instead, they submitted "Design Drawings" and subtle errors or changes made when the road was built, could possibly be the reason.

Does anyone know for sure?

This would be a reasonable explanation for some of the quirky behaviors I observed on my GPS driving on the loop 101 where it keeps telling me I'm on the side road instead of the freeway.

road lock

jale wrote:

This would be a reasonable explanation for some of the quirky behaviors I observed on my GPS driving on the loop 101 where it keeps telling me I'm on the side road instead of the freeway.

That's probably road lock. If you deviate off-route slowly off a road that runs parallel to the one you were on, it will think you're still on the routed road. Once you diverge past some threshold it will finally pick it up. If it bugs you, you can cancel and restart the route.

The other way around

saxmaniac wrote:
jale wrote:

This would be a reasonable explanation for some of the quirky behaviors I observed on my GPS driving on the loop 101 where it keeps telling me I'm on the side road instead of the freeway.

That's probably road lock. If you deviate off-route slowly off a road that runs parallel to the one you were on, it will think you're still on the routed road. Once you diverge past some threshold it will finally pick it up. If it bugs you, you can cancel and restart the route.

Actually, it was the opposite: My route was to be on the freeway and the GPS kept telling to get on it -- for several miles. I even tried to go to the left lane to see if it would see the difference.

GPS averaging

I watched my gps for a while and confirm that after the first few minutes the accuracy continued to vary.